Certain types of printing systems are adapted for printing images on large-scale substrates, such as for museum displays, billboards, sails, bus boards, and banners. Some of these systems use so-called drop on demand ink jet printing. In these systems, a carriage which holds a set of print heads scans across the width of the substrate while the print heads deposit ink as the substrate moves.
Some of these systems use different colored inks to create the desired images. For instance, black, yellow, cyan, and magenta colored inks are commonly employed alone or in combination to generate the image. Other systems use additional colored inks, such as light black, light yellow, light cyan, and light magenta to create images with higher resolution. In general, images created with a greater number of colored inks are typically of higher quality than those generated with fewer colored inks.
Certain applications require a printing system that has different modes of operation, for example, one mode enables printing images at high speeds, and another mode enables the system to print higher quality images at a lower speed. In these systems, certain print heads, as well as the ink transmission lines connected to the print heads, must be removed and exchanged when switching the printing system from one mode of operation to the other mode.
Such printing systems have been accepted in the industry, and they are presumably considered to perform reasonably well for their intended purpose. However, it is desirable, in some circumstances, to be able to switch the type (e.g. color or fast drying versus slow drying ink) of the ink which is transmitted to a particular print head without having to remove the print head and the corresponding transmission line which transmits the ink from an ink reservoir to the print head.
The present invention greatly reduces problems encountered by the aforementioned prior art printing systems. The present invention provides an efficient printing system which is capable of printing high quality images with several colored inks and printing images at greater speeds with fewer colored inks.
In one aspect, the present invention implements a printing apparatus for printing images on a substrate that has two modes of operation. The printing apparatus is provided with a first print head connected to a selector valve which in turn is connected to at least a pair of reservoirs. The first reservoir holds one colored ink while the another reservoir holds a different colored ink. The selector valve has at least two selectable states. The first state facilitates transmitting ink from one of the reservoirs to the print head, and the second state facilitates transmitting ink from the other reservoir to the print head. The selector valve can be coupled to a controller which is computer operated. Alternatively, the controller can be manually operated.
Embodiments of this aspect of the invention can have one or more of the following features. The printing system includes a second print head which receives ink directly from the second reservoir. Alternatively, the second print head can be connected to the selector valve such that the second print head receives ink from the first reservoir when the selector valve is in the first state and receives ink from the second reservoir when the selector valve is in the second state. In this arrangement, there can be a second pair of print heads which receive ink directly from the second reservoir.
Optionally, there can be one or more additional sets of print heads, and an equal number of additional selector valves and additional pairs of reservoirs. Each set includes two pair of print heads: one pair of print heads receives ink directly from one of the reservoirs of the respective pair of reservoirs, and the other pair of print heads is connected to a respective selector valve which in turn is connected to the other reservoir of the respective pair of reservoirs. Here again, each selector valve has two states which enables transmitting ink from either reservoir to the pair of print heads connected to the selector valve.
In one embodiment, there is a total of sixteen print heads, four selector valves, and four pairs of ink reservoirs. The first reservoir and the second reservoir of the first pair of reservoirs holds light black ink, and dark black ink, respectively; the first reservoir and the second reservoir of the second pair of reservoirs holds light yellow ink, and dark yellow ink, respectively; the first reservoir and the second reservoir of the third pair of reservoirs holds light cyan ink, and dark cyan ink, respectively; and the first reservoir and the second reservoir of the fourth pair of reservoirs holds light magenta ink, and dark magenta ink, respectively.
In some embodiments, the second set of print heads is positioned between the first pair and the second pair of the first set of print heads, the third set of print heads is positioned between the first pair and the second pair of the second set of print heads, and the fourth set of print heads is positioned between the first pair and the second pair of the third set.
In ceratin embodiments, the first pair and the second pair of the second set are positioned adjacent to the first pair and the second pair of the first set, respectively; the first pair and the second pair of the third set are positioned adjacent the first pair and the second pair of the second set, respectively; and the first pair and the second pair of the fourth set are positioned adjacent to the first pair and the second pair of the third set, respectively, so that the first pair and the second pair of fourth set are also positioned adjacent to each other.
In certain embodiments, the printing system includes a flushing mechanism to cleanse the selector valve and the transmission lines when the selector valve is switched from the first state to the second state or vice versa. The system can be flushed before the selector valve is changed, or, alternatively, after it is switched to a different state.
Related aspects include a method of printing images on a substrate. The method includes depositing a first ink or a second ink from a first print head, and selecting between a first state of operation and a second state of operation. When in the first state of operation a first reservoir holding the first ink is in fluid communication with the first print head, and when in the second state of operation a second reservoir holding the second ink is in fluid communication with the first print head.
Some embodiments may have one or more of the following advantages. The printing system can be switched from a high-quality operation to a high-speed operation in a relatively short period of time, for example, in just a few minutes. The entire switching operation can be automated without manual intervention. Thus, nothing has to be manually removed from the printing system to switch the operating mode of the system.